Indirectly-heated cathodes



Nov. 26, 1957 L. w. GEIER I INDIRECTLY-HEATED CATHODES Filed Aug 28.1952 F'IG.

/r////////M///////////////M/ /NVENTO/? LEONA/2D W. GE/El? -Mm ATTORNE V2,814,754 [Qfi Patented Nov. 26, 19 7 INDIRECTLY-HEATED CATHODES LeonardW. Geier, Nafick, Mass., assignor to Raytileon Manufacturing Company,Newton, Mass., a corporation of Delaware Application August 28, 1952,Serial No. 306,872

2 Claims. (Cl. 313-346) This invention relates to electron dischargedevices and more particularly to cathodes of the indirectly-heated typewhich may be used in electron discharge devices.

Indirectly-heated cathodes having a reservoir of electron-emissivematerial positioned beneath a porous tungsten surface are well known.This invention relates to an improvement in the reservoir type cathode,but is not necessarily limited thereto.

Specifically, this invention discloses that the reservoir ofelectron-emissive material may be made of a metallic mesh with theelectron-emissive material packed into the spaces between the mesh. Themesh, which may be made, for example, of molybdenum, is attached to acentral support member and is in substantial contact with the porousmember which covers the reservoir. By the use of this structure, theelectron-emissive material in the reservoir will be firmly held duringassembly of the device and will be uniformly activated during processingof the device due to even conduction of heat to all regions of thereservoir by means of the metallic mesh. Furthermore, heat may beuniformly transferred from the central support member to the poroustungsten member covering the reservoir by means of the metallic mesh sothat the exterior surface of the cathode is maintained at asubstantially uniform heat. This reduces the possibility of localizedheating attendant upon localized production of gas, which increaseslocalized back bombardment of the cathode, particularly in high voltagedevices, such as magnetrons.

This invention further discloses a lock nut arrangement whereby thecathode end shields may be locked on to the base support member, therebyrigidly holding the porous tungsten member with respect to the basesupport member and the reservoir.

Other objects and advantages of this invention will become apparent asthe description thereof progresses, reference being had to Figs. 1 and2, wherein:

Fig. 1 illustrates a longitudinal cross-sectional view of a cathodeembodying this invention; and

Fig. 2 illustrates a transverse cross-sectional view of the device shownin Fig. 1 taken along line 2--2 of Fig. 1.

Referring now to Figs. 1 and 2, there is shown a cathode structure 10comprising a base support cylinder 11, which is rigidly attached at itslower end to a lead-in support member 12, which is adapted to be sealedby means of an insulating seal, not shown, through the wall of anelectron discharge device. The outer surface of support cylinder 11 hasa cylindrical recess therein for a substantial distance along thelongitudinal dimension thereof. Positioned in the recess in member 11 isa wire mesh 13 which is attached to support cylinder 11 as, for example,by sintering. The spaces in wire mesh 13 are filled with anelectron-emissive material 14, which may be, for example, originallybarium carbonate, which, upon heating, breaks down to electron-emissivebarium oxide during activation of the cathode.

It is to be clearly understood that any desired electronemissivematerial may be used in place of the barium carbonate 14. The bariumcarbonate 14 is preferably applied to the mesh 13 as a paste duringassembly of the device, but other methods may be used if it is sodesired.

Surrounding base cylinder 11 and the mesh 13 is a cylindrical member 15,which may be made, for example, of porous tungsten. As shown here, themember 15 engages the mesh 13 and the member 11 beyond the ends of therecess containing mesh 13. The member 15 may be produced, for example,by sintering powdered tungsten in a mold or by any other desired means.Furthermore,

other porous metals could be used for member 15, such as porousmolybdenum or porous tantalum. Member 15 is rigidly held with respect tomember 11 by engaging at its lower end a recess 16 in lead-in member 12.A larger recess 17 in member 12, positioned above the recess 16,produces a cylindrical extension 18 of lead-in member 12 which extendsupwardly along member 15, spaced therefrom, to a point somewhat belowthe lower edge of the recess in member 11 containing the mesh 13. Theextension 18 would be used as a cathode end shield in a magnetron andwould be positioned just below the lower edge of the anode members toprevent any substantial motion of the electrons in a direction axial tothe cathode.

The upper end of porous member 15 engages a recess 19 in an upper endshield member 20, which threadedly engages base support cylinder 11 asat 21. An extension 22 of shield member 20 extends downwardly aroundporous cylindrical member 15 spaced therefrom to a point somewhat abovethe upper edge of the recess in member 11 which contains the mesh 13.Extension 22 would act as the upper end shield proper if the cathodewere used in a magnetron and would terminate at a point slightly abovethe upper edge of the anode members. A lock nut 23 is provided, whichthreadedly engages member 11 and bears against the upper edge of endshield 20, thereby locking the cathode assembly together. A heater coil24 is provided within cylinder 11, which is hollow. The heater coil 24is shown here by way of example only, and any desired means for heatingthe cathode may be used. The upper end of the heater coil 24 is rigidlyattached as by welding to a rod 25, which, in turn, is rigidly attachedas by welding through plug 26 to the upper end of cylinder 11. The lowerend of heater coil 24 is welded to a heating rod 27 which extendsdownwardly through lead-in cylinder 12 spaced therefrom and through aninsulating seal, not shown. By application of a potential betweenlead-in rod 27 and lead-in member 12, current may be caused to flowthrough heater coil 24, thereby heating the coil 24. The heat from coil24 is, in turn, radiated to support cylinder 11 which transfers the heatby conduction through the mesh 13 to the electronemissive material 14and the porous tungsten cylinder 15. The electron-emissive material 14slowly diffuses through the porous cylinder 15, thereby creating acondition on the surface of porous cylinder 15 which will cause copiousemission of electrons. When such a device is constructed with bariumcarbonate as the electron-emissive material, good results may beobtained with the cathode heated to a temperature of approximately 1000C.

This completes the description of the embodiment of the inventionillustrated herein. However, many modifications thereof will be apparentto persons skilled in the art without departing from the spirit andscope of the invention. For example, the support member 11 and porousmember 12 need not necessarily be cylindrical and the device could beused without end shields, if so desired. Accordingly, it is intendedthat this invention be not limited to the particular details of theembodiment of the invention disclosed herein, except as defined by thedependent claims.

What is claimed is:

1. An indirectly-heated cathode comprising a support member, a Wire meshcovering the surface of said member, electron-eniissive materialsubstantially filling the 4 in said cylinder, an end shield covering oneend of said porous cylinder and threadedly attached to said supportcylinder, and a lock nut threadedly engaging said support cylinder andbearing against said end shield.

spaces in said mesh, a porous member covering said mesh, 5

and an end shield covering one end of said porous mem- References Citedin the file Of this Patent belr alrid tllrielrladecidlydzlittachedtosaidi support membker, ant: UNITED STATES A E S a oc nu rea e y engagingsai support mern er an bearing against said end shield. und 2. Anindirectly-heated cathode comprising a metallic 10 2107945 i n 1938support cylinder, a mesh covering the surface of said mem- 5 5 a e 1947ber and attached thereto, electron-emissive material com- 2447038 1948prising barium substantially filling the spaces in said mesh, 2543728 27 g 1951 a porous tungsten cylinder member covering said mesh 2673277 ns6 A in substantial contact therewith, a heater positioned with- 15emmens et a 195

2. AN INDIRECTLY-HEATED CATHODE COMPRISING A METALLIC SUPPORT CYLINDER,A MESH COVERING THE SURFACE OF SAID MEMBER AND ATTACHED THERETO,ELECTRON-EMISSIVE MATERIAL COMPRISING BARIUM SUBSTANTIALLY FILLING THESPACES IN SAID MESH, A POROUS TUNGSTEN CYLINDER MEMBER COVERING SAIDMESH IN SUBSTANTIAL CONTACT THEREWITH, A HEATER POSITIONED WITHIN SAIDCYLINDER, AN END SHIELD COVERING ONE END OF SAID POROUS CYLINDER ANDTHREADEDLY ATTACHED TO SAID SUPPORT CYLINDER, AND A LOCK NUT THREADEDLYENGAGING SAID SUPPORT CYLINDER AND BEARING AGAINST SAID END SHIELD.